1. Field of the Invention
The present invention relates to a flat panel display device that includes an organic thin film transistor (TFT) in which a pattern failure of an organic semiconductor layer in the organic TFT can be avoided by preventing a step difference between the source and the drain electrodes and the substrate, a method of manufacturing the organic TFT, and a flat panel display device having the organic TFT.
2. Description of the Related Art
Organic TFTs are considered to be next generation driving devices, and many studies of organic TFTs are being conducted. Organic TFTs use an organic film instead of a silicon film as a semiconductor layer, and the organic film can be formed via a printing process under atmospheric pressure instead of using a plasma enhanced chemical vapor deposition (PECVD) process, which is used for forming ordinary silicon thin films. An organic TFT can be manufactured in a roll to roll process using a plastic substrate at a low cost.
An organic TFT that uses an organic film as the semiconductor layer has drawn attention as a switching device for a flexible organic electroluminescent display device since organic TFTs can be manufactured at a low temperature. A pentacene TFT with high hole mobility and a method of manufacturing the pentacene TFT that reduces the time for depositing a thin film is disclosed in Korean Patent Publication No. 2004-0028010 The structure of an organic TFT with good electrical performance and a method of manufacturing the organic TFT are disclosed in Korean Patent Publication No. 2002-0084427. Also, a TFT with high carrier mobility and high on/off current ratio due to a channel region formed of an organic compound having a radical is disclosed in Japanese Patent Publication No. 2003-92410.
Organic TFTs are classified into low molecular organic TFTs with an organic film formed of a low molecular organic material, such as oligothiophene, pentacene, etc., and polymer organic TFTs with an organic film formed of a polymer organic material, such as a polythiophene group. Alsox, organic TFTs can be classified into top gate type TFTs, in which a gate is arranged on an organic semiconductor layer, and bottom gate type TFTs, in which the gate is arranged under the organic semiconductor layer.
An organic TFT includes source and drain electrodes formed on a substrate, an organic semiconductor layer formed on the source and drain electrodes, a gate insulating film formed on the organic semiconductor layer, and a gate electrode formed on the gate insulating film. After the source and drain electrodes are formed on the substrate, the organic semiconductor layer and the gate insulating film are formed by coating or deposition. Specifically, when the organic semiconductor layer is formed by coating, if the source and drain electrodes are formed as thick metal wires, the organic semiconductor layer must be coated to a thickness equal to or greater than the thickness of the metal wires. A portion of the organic semiconductor layer between the source and drain electrodes serves as a channel region. Therefore, if the organic semiconductor layer is too thick, the channel layer may not become properly conductive, or a high driving voltage must be applied to make the channel layer conductive.
Therefore, the organic semiconductor layer must be sufficiently thin so that the channel layer readily becomes conductive through the application of a predetermined driving voltage. When the organic semiconductor layer is thinner than the source and drain electrodes of metal wires, an edge portion of the source and drain electrodes can experience electrostatic discharge or can cause a pattern failure of a semiconductor layer due to poor step coverage, thus causing a disconnection of wires in the channel region. What is needed is an improved design for an organic TFT and a flat panel display using the organic TFT that overcomes these problems.